将SecWebSocketProtocol标头（SubProtocol）添加到ASP Web API 2中的WebSocketHandler

Question

在ASP Web API中，升级到WebSocket需要初始化Microsoft.Web.WebSockets.WebSocketHandler。这种类型的WebSocket没有提供添加SecWebSocketProtocol标头的选项，这对我的情况很重要（MQTT超过WebSockets）。

public HttpResponseMessage Get()
{
    if (HttpContext.Current.IsWebSocketRequest || HttpContext.Current.IsWebSocketRequestUpgrading)
    {
       HttpContext.Current.AcceptWebSocketRequest(new WebSocketHandler());
       return Request.CreateResponse(HttpStatusCode.SwitchingProtocols);
    }

    else return new HttpResponseMessage(HttpStatusCode.BadRequest);
}

如何将此字段添加到WebSocketHandler？